Q. 515.0( 1 Vote )

# If the focus of a parabola is (0, –3) and its directrix is y = 3, then its equation isA. x2 = –12yB. x2 = 12yC. y2 = –12xD. y2 = 12x

As focus lies on y – axis,

Equation is x2 = 4ay or x2 = -4ay,

Focus has a –ve co = ordinate, so equation is x2 = -4ay,

Co – Ordinate of focus = (0, -a)

-a = -3

a = 3

As per the equation,

x2 = -4ay

x2 = -4 (3) y

x2 = -12y

Hence, the required equation is x2 = -12y.

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